Abstract: The present invention relates to a transmission system for a two-wheeled cycle of the type comprising at least one sprocket (1) attached to the rear wheel hub (2) and rotatably mounted around an axis (x); at least one chainring (3) secured to the frame of the cycle and rotatably mounted around a second axis (y) parallel to the axis (x); a crankset composed of two pedals (7, 8) rotatable around a third axis (z) parallel to the axes (x, y) and located inside the rear wheel; and a main transmission element (6) drivable by actuating the crankset and passing through said sprocket (1) and also passing through, or controlled by, said chainring (3).